14 ' J. O. HAGSTEOM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



important distinguishing marks employable to the systematist. Especially the stem- 

 anatomy is rather uniform. 



Five species are known which should be divided in two subsections. 



Subsectio 1. Filiformes Hagstr. 

 Fructus rostro brevissimo verrucseformi. 



P. fllif oralis Pbrsoon, Syn. plant. I. (1805), 152. 



P. setaceus Schum., Enum. plant. Saell. I, 1801, 51 (non L.). — P. horealis 

 Rafin. in Med. Reposit. 1808, 354? — P. maritimus Pohl, Tent. El. Bohem. I, 1810, 

 159 ex Graebner, Potamog. in Engler, Pflanzenr. IV, 11, 1907,126.' — P. fascicula- 

 tus WoLFG. in J. A. et J. H. Schultes, Mant. in vol. Ill syst. veg. 1827, 364—365. 

 — P. marinus L. ex Fr., Novitise El. suec. 1828, 54. — P. salinus Schur, Phytogr. 

 Eragm. CII, in Osterr. Bot. Zeitschr. n. 9, 1870, 280 (nomen solum). — P. capilla- 

 ceus MoERCK, Herb. Mus. Brit. 1821 ex Ar. Benn. in Journ. of Bot. 1890, 301 (nomen 

 solum). — Eigs. 3 and 4. 



The expression of P. Bocconi, that Linne is said to have used, though not in the 

 Olandska och Gotl. Resan 1745, 221, must not be understood as a species-name but 

 only as a reference to the Eig. 5. tab. 20 in Boccone, Icones et descr. etc. and is 

 an abbreviation instead of »Pota77iogeton pusilhmi fhiitans Bocco7ii». 



By the authority of Prof. E. Eries the name marinus has been employed quite 

 up to our days (Hartman, Handb. 1879; Richter, PI. eur. 1890). Before Eries it 

 was applied to some forms of P. pectinatus (Ltnnb, Roth, Schumacher, Flora Da- 

 nica, Lamarck & De Candolle, Smith, Hartman, Wahlenberg and others) or to 

 forms belonging both to pectinatus and filiformis (Allionius, El. pedem. ex synon.). 



P. filiformis has often been mixed up with P. pectinatus and considered as a 

 variety or subspecies of it (Hooker, Stud. fl. Brit. Isl. 1878). Even as late as in 

 1894 K. Schumann hesitatingly designates it as a distinct species (Elora brasil. Ill, 

 3, 696) and P. Graebner comprehends pectinatus, vaginatns, amblyopliyllus, filiformis 

 and pamiricus to a species collectiva >P. pectinatusi^ (Potamog. 1907, 121); so still in 

 the Synopsis mitteleur. El. 1913, 538. G. Eischer certainly separates it from P. 

 pectinatus, but regards it together with P. juncifolius as subspecies of a collective 

 species -imarimis autt. » (Die bayer. Potamog. 1907, 130). 



No doubt P. filiformis is an independent species and well distinguished from 

 P. pectinatus. Beside the differences mentioned by S. Almquist, G. Eischer and 

 others, the most important of which, of course, pertain to the style and stigma (fig. 

 Z, A), the fruit, the small perianth- leaves and the inflorescence, the dark- bordered 

 connate sheaths (fig. 3, B) and obtuse leaves (fig. 3, E-H), we must also observe 

 that the pollengrains are smaller and the hybrids of the two species always sterile. 



^ Yet it is uncertain if P. filiformis is liere concerned. The name may have been adopted after Plu- 

 KENETii description in Almagestum botanicum 1696: P. maritimicm ramosissimum etc. or it may simply be a 

 misprint. 



